Torsion properties of adult human cortical bone are being restudied by means of a type of test specimen never before used for bone. Cross sections of these specimens will be analyzed for the percentage of spaces, secondary osteons, fragments of osteons, and interstitial lamellae in the break area. The number of osteons and of osteon fragments/mm2 and the area (mm2) per osteon and per osteon fragment will also be made. These data will be used for explaining differences found in the torsion properties of the specimens. Tensile properties and histological structure of standardized specimens of cortical bone from adult women are being determined. These results will be evaluated for age differences and compared with similar data from men of comparable age. Similar studies on specimens from different races are in progress. Special testing and strain measuring techniques are being developed for use with small, thin specimens. Material is being collected for studying mechanical properties of bone of a single histological type. BIBLIOGRAPHIC REFERENCES: Evans, F.G. and Vincentelli, R., Relations of the compressive properties of human cortical bone to histological structure and calcification. J. Biomechanics 7: 1-10, 1974. Evans, F.G., The mechanical properties of human cortical bone, Accademia Nazionale dei Lincei, Quad. N. 208, Rome, 1974.